| 摘要 |
PURPOSE:To prevent a detection value from being varied even when an environmental temperature is varied by detecting a contrast by executing a movement by a command value prescribed number of times, continuing a case division, while storing a detection position and the contrast, and finally, calculating a focal position by bringing the relation of the contrast of each position and the position to curve approximation. CONSTITUTION:A focal position is detected by bringing a placing table 91 for placing an object body 90 to prescribed movement by a prescribed distance determined in advance within the limit of a prescribed number of times determined in advance, and also, detecting and holding a contrast and position information in each moving position, bringing the relation of the contrast and the position information to the curve approximation, and calculating the focal position based on the curve. Accordingly, the focal position can be detected by only the movement of the placing table 91 within the prescribed number of times, and also, when an abnormal operation occurs due to a noise, etc., it can be detected as an error, and it can be brought to an end automatically. In such a way, even when a backlash of a focusing driving source and a hysteresis characteristic are brought to temperature variation, the focal position can be detected with high accuracy. |
